Nerve Function Tests for Evaluating Low Back Problems

Topic Overview

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Sensory testing

Just as your muscles receive signals through certain nerves, other
nerves carry signals back to your spinal cord from specific sections of your
skin and other tissues. Testing your sense of feeling helps your doctor find
out what nerve root may be compressed.

Your sense of feeling may be tested in several ways. Your doctor will
probably ask you to close your eyes during this testing, because it's easy to
imagine the feeling if you can see the test being done. Testing may include
touching your skin lightly with a cotton ball or pricking your skin lightly
with a pin.

Areas that send messages through particular nerves

Area of skin

Nerve level

The front of your thigh

L1, L2, L3, L4

The inside of your lower leg, from the knee to the inner ankle and
arch

L4

The top of your foot and toes

L5

The outside of your ankle and foot

S1

Reflexes

Tendons attach the muscles to the bones. Reflexes are little movements of the muscle when the tendon is tapped. A reflex can be decreased or absent if there is a problem with the nerve supply. To test your reflexes, your doctor will use a rubber hammer to tap firmly on the tendon. If
certain reflexes are decreased or absent, it will show what nerve might be
compressed. Not all nerve roots have a reflex associated with
them.

Patellar tendon reflex. You sit on the exam table
with your knee bent and your foot hanging down, not touching the floor. Your
doctor will use a rubber hammer to tap firmly on the tendon just below your
kneecap. In a normal test, your knee will extend and lift your foot a little. A
decreased or absent reflex may mean that there is compression in the L2, L3, or L4 region.

Achilles tendon reflex. You sit on a table with your
knees bent and feet hanging down, or you may be asked to lie down on your
stomach with your legs straight and your feet off the edge of the exam table.
Your doctor will use a rubber hammer to tap firmly on the Achilles tendon,
which connects the muscle at the back of your calf to your heel bone. In a
normal test, your foot will move as though you were going to point your toes. A
decreased or absent reflex may mean that there is compression in the S1 region.